Monitoring and tracking bipolar ablation

ABSTRACT

Methods and systems treat abnormal cardiac electrical activity employing a probe having first and second ablation electrodes disposed on a distal portion of the probe and a sensing electrode disposed between the first and second ablation electrodes, bringing the probe into contact with cardiac tissue, and applying energy through the first and second ablation electrodes to ablate target tissue along an ablation path, monitoring cardiac electrical activity using the sensing electrode to detect the cardiac electrical activity. After making an observation that the cardiac electrical activity is no longer detectable by the sensing electrode, energy application is terminated.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to invasive medical devices. More particularly,this invention relates to ablation of tissue using such devices.

2. DESCRIPTION OF THE RELATED ART

Ablation of body tissue using electrical energy is known in the art. Theablation is typically performed by applying alternating currents, forexample radiofrequency energy, to electrodes, at a sufficient power todestroy target tissue. Typically, the electrodes are mounted on thedistal tip of a catheter, which is inserted into a subject. The distaltip may be tracked in a number of different ways known in the art, forexample by measuring magnetic fields generated at the distal tip bycoils external to the subject. The catheter may be provided withunipolar or bipolar ablation electrodes.

Kratoska, U.S. Patent Application Publication No. 20080275440 isdirected to a method of providing feedback regarding the outcome ofablation therapy. A method is provided for obtaining feedback regardingthe results of tissue ablation, the method comprising deploying one ormore needles from a catheter into a target tissue, delivering energy viaat least one of the one or more needles to ablate at least a portion ofthe target tissue to form a lesion, stopping energy delivery via the atleast one of the one or more needles, and measuring a tissue propertyvia at least one of the one or more needles after the energy deliveryhas been stopped. The measured tissue property may be temperature orimpedance. Also, the measured tissue property may be used to determine avolume of the lesion formed by ablation therapy.

SUMMARY OF THE INVENTION

There is provided according to embodiments of the invention a method fortreating abnormal cardiac electrical activity, which is carried out byproviding a probe having first and second ablation electrodes disposedon a distal portion of the probe and a sensing electrode disposedbetween the first and second ablation electrodes, bringing the probeinto contact with a target tissue in a heart of a subject, and applyingenergy through the first and second ablation electrodes to ablate thetarget tissue along an ablation path. The method is further carried outby while applying energy, monitoring cardiac electrical activity usingthe sensing electrode to detect the cardiac electrical activity, makingan observation that the cardiac electrical activity is no longerdetectable by the sensing electrode, and responsively to the observationterminating energy application.

According to another aspect of the method, the cardiac electricalactivity is near-field activity.

According to yet another aspect of the method, there is a phase shift of90° between an E field and an H field of the cardiac electricalactivity.

According to still another aspect of the method, applying energyincludes alternating between a bipolar mode of operation wherein thefirst and second ablation electrodes function as bipolar electrodes anda unipolar mode of operation wherein at least one of the first andsecond ablation electrodes functions as a unipolar electrode.

Yet another aspect of the method includes monitoring applying energy bygraphically displaying a map of a portion of the heart that includes thetarget tissue and a progression of energy application along the ablationpath.

According to an additional aspect of the method, applying energy alsoincludes alternating between a bipolar mode of operation wherein thefirst and second ablation electrodes function as bipolar electrodes anda unipolar mode of operation wherein at least one of the first andsecond ablation electrodes functions as a unipolar electrode, andwherein monitoring cardiac electrical activity includes tagging the mapto indicate first and second portions of the ablation path associatedwith the bipolar mode of operation and the unipolar mode of operation,respectively.

According to one aspect of the method, the probe has at least twosensing electrodes disposed between the first and second ablationelectrodes.

There is further provided according to other embodiments of theinvention apparatus for carrying out the above-described method.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto the detailed description of the invention, by way of example, whichis to be read in conjunction with the following drawings, wherein likeelements are given like reference numerals, and wherein:

FIG. 1 is a pictorial illustration of a system for performing ablativeprocedures, which is constructed and operative in accordance with adisclosed embodiment of the invention; and

FIG. 2 is an electroanatomical map in the postero-anterior projection ofa heart undergoing ablation according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the various principles ofthe present invention. It will be apparent to one skilled in the art,however, that not all these details are necessarily always needed forpracticing the present invention. In this instance, well-known circuits,control logic, and the details of computer program instructions forconventional algorithms and processes have not been shown in detail inorder not to obscure the general concepts unnecessarily.

Aspects of the present invention may be embodied in software programmingcode, which is typically maintained in permanent storage, such as acomputer readable medium. In a client/server environment, such softwareprogramming code may be stored on a client or a server. The softwareprogramming code may be embodied on any of a variety of knownnon-transitory media for use with a data processing system, such as adiskette, hard drive, electronic media or CD-ROM. The code may bedistributed on such media, or may be distributed to users from thememory or storage of one computer system over a network of some type tostorage devices on other computer systems for use by users of such othersystems.

System Description

Turning now to the drawings, reference is initially made to FIG. 1,which is a pictorial illustration of a system 10 for performing ablativeprocedures on a heart 12 of a living subject or patient, which isconstructed and operative in accordance with a disclosed embodiment ofthe invention. The system comprises a catheter 14, which ispercutaneously inserted by an operator 16 through the patient's vascularsystem into a chamber or vascular structure of the heart 12. Theoperator 16, who is typically a physician, brings the catheter's distaltip 18 into contact with the heart wall at an ablation target site.Electrical activation maps may then be prepared, according to themethods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and incommonly assigned U.S. Pat. No. 6,892,091, whose disclosures are hereinincorporated by reference. One commercial product embodying elements ofthe system 10 is available as the CARTO® 3 System, available fromBiosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif.91765.

Areas determined to be abnormal, for example by evaluation of theelectrical activation maps, can be ablated by application of thermalenergy, e.g., by passage of radiofrequency electrical current throughwires in the catheter to one or more electrodes at the distal tip 18,which apply the radiofrequency energy to the myocardium. The energy isabsorbed in the tissue, heating it to a point (typically about 50° C.)at which it permanently loses its electrical excitability. Whensuccessful, this procedure creates non-conducting lesions in the cardiactissue, which disrupt the abnormal electrical pathway causing thearrhythmia. The principles of the invention can be applied to differentheart chambers, to mapping in sinus rhythm, and when to treat manydifferent cardiac arrhythmias.

Unipolar ablation creates relatively deep lesions that are centered onthe location of the ablation electrode, while bipolar ablation tends tocreate shallower, elongated lesions extending between a pair of bipolarelectrodes. The nature and location of these bipolar lesions can createdifficulty in lesion assessment and tracking.

The catheter 14 typically comprises a handle 20, having suitablecontrols on the handle to enable the operator 16 to steer, position andorient the distal end of the catheter as desired for the ablation. Toaid the operator 16, the distal portion of the catheter 14 containsposition sensors (not shown) that provide signals to a positioningprocessor 22, located in a console 24.

Ablation energy and electrical signals can be conveyed to and from theheart 12 through one or more ablation electrodes 32 located at or nearthe distal tip 18 via cable 34 to the console 24. Pacing signals andother control signals may be conveyed from the console 24 through thecable 34 and the electrodes 32 to the heart 12. Sensing electrodes 33,also connected to the console 24 are disposed between the ablationelectrodes 32 and have connections to the cable 34. During ablation theablation electrodes 32 are typically operated in a bipolarconfiguration. However, one or both of them may be operated as unipolarelectrodes using configuration circuitry for varying the mode ofoperation between a bipolar and a unipolar mode as required during anablation.

Wire connections 35 link the console 24 with body surface electrodes 30and other components of a positioning sub-system. The electrodes 32 andthe body surface electrodes 30 may be used to measure tissue impedancemeasuring at the ablation site as taught in U.S. Pat. No. 7,536,218,issued to Govari et al., which is herein incorporated by reference. Atemperature sensor 37, typically a thermocouple or thermistor, ismounted on or near each of the electrodes 32.

The console 24 typically contains one or more ablation power generators25. The catheter 14 may be adapted to conduct ablative energy to theheart using any known ablation technique, e.g., radiofrequency energy,ultrasound energy, and laser-produced light energy. Such methods aredisclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and7,156,816, which are herein incorporated by reference.

The positioning processor 22 is an element of a positioning sub-systemof the system 10 that measures location and orientation coordinates ofthe catheter 14.

In one embodiment, the positioning sub-system comprises a magneticposition tracking arrangement that determines the position andorientation of the catheter 14 by generating magnetic fields in apredefined working volume its vicinity and sensing these fields at thecatheter using field generating coils 28.

As noted above, the catheter 14 is coupled to the console 24, whichenables the operator 16 to observe and regulate the functions of thecatheter 14. Console 24 includes a processor, preferably a computer withappropriate signal processing circuits. The processor is coupled todrive a monitor 29. The signal processing circuits typically receive,amplify, filter and digitize signals from the catheter 14, includingsignals generated by the above-noted sensors and a plurality of locationsensing electrodes (not shown) located distally in the catheter 14. Thedigitized signals are received and used by the console 24 and thepositioning sub-system to compute the position and orientation of thecatheter 14 and to analyze the electrical signals from the electrodes.

Typically, the system 10 includes other elements, which are not shown inthe figures for the sake of simplicity. For example, the system 10 mayinclude an electrocardiogram (ECG) monitor, coupled to receive signalsfrom one or more body surface electrodes, so as to provide an ECGsynchronization signal to the console 24. As mentioned above, the system10 typically also includes a reference position sensor, either on anexternally-applied reference patch attached to the exterior of thesubject's body, or on an internally-placed catheter, which is insertedinto the heart 12 maintained in a fixed position relative to the heart12. Conventional pumps and lines for circulating liquids through thecatheter 14 for cooling the ablation site are provided.

The catheter 14 typically includes one or more pairs of ablationelectrodes 32 as shown in FIG. 1, with one or more of the sensingelectrodes 33 disposed between each pair of the ablation electrodes 32.Typically, the ablation electrodes 32 have a large area in order toeffectively deliver RF power to the tissue, while the sensing electrodes33 may be relatively smaller, as shown in the figure. In the ringelectrodes shown in FIG. 1, the ablation electrodes 32 should be widerthan the sensing electrodes 33.

Although the pictured embodiment includes two ring electrodesside-by-side, it is also possible to use a single sensing electrode orto use a single split ring to serve as a pair of sensing electrodes. Thesensing electrodes 33 sense local electrical activity in the heart, and,with the aid of suitable detection and monitoring circuitry (not shown)in the console 24, track the progress of lesion formation by detecting adrop in the electrical amplitude. For this purpose, a pair of sensingelectrodes is preferable, since it enables bipolar measurement ofnear-field electrical signals (having a phase shift of 90° between the Efield and H field, so that no energy is transported and hence gives amore accurate indication of local electrical activity. Complete ablationis indicated by extinguishment of the local electrical activity. It ispossible to dynamically reconfigure the ablation electrodes 32 tooperate selectively in bipolar mode and unipolar mode according to thelocal requirements of the lesion required to be generated.

Ablation Monitoring

Bipolar ablation may optionally be tracked graphically as it proceedsalong a path, so that the operator can readily determine when a line orannulus has been completely ablated. Reference is now made to FIG. 2,which is a prospective example of an electroanatomical map 37 in thepostero-anterior projection of a heart undergoing ablation according toan embodiment of the invention. The above-noted CARTO 3 system iscapable of producing such maps. In this example, regions containingganglionated plexi are outlined by circles 39. These regions would guidethe selection of a position and orientation of a lesion 41 to beestablished by ablation in order to treat an arrhythmia, for example anarrhythmia associated with complex fractionated atrial electrograms.Techniques for localizing and treating of such arrhythmias are taught incommonly assigned copending application Ser. No. 12/275,380, which isherein incorporated by reference. Of course, many other arrhythmias andaberrant conduction paths may be treated according to the principles ofthe invention.

As ablation proceeds, the process is tracked and displayed on the map 37as a series of connected tags, in which rectangles 43 havingcross-hatched patterns represent intervals of bipolar ablation, andrectangles 45, generally oriented perpendicular to the rectangles 43represent intervals of unipolar ablation. The lesion 41 appears linear;however this is not necessarily the case. Such lesions may becurvilinear, or even discontinuous. The rectangles 43 may bedistinguished from the rectangles 45, for example by graphicaltechniques, e.g., color.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and sub-combinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. A method for treating abnormal cardiac electrical activity,comprising the steps of: providing a probe having first and secondablation electrodes disposed on a distal portion of the probe and asensing electrode disposed between the first and second ablationelectrodes; bringing the probe into contact with a target tissue in aheart of a subject; applying energy through the first and secondablation electrodes to ablate the target tissue along an ablation path;while performing the step of applying energy, monitoring cardiacelectrical activity using the sensing electrode to detect the cardiacelectrical activity; making an observation that the cardiac electricalactivity is no longer detectable by the sensing electrode; andresponsively to the observation terminating the step of applying energy.2. The method according to claim 1, wherein the cardiac electricalactivity is near-field activity.
 3. The method according to claim 2,wherein there is a phase shift of 90° between an E field and an H fieldof the cardiac electrical activity.
 4. The method according to claim 1,wherein applying energy comprises alternating between a bipolar mode ofoperation wherein the first and second ablation electrodes function asbipolar electrodes and a unipolar mode of operation wherein at least oneof the first and second ablation electrodes functions as a unipolarelectrode.
 5. The method according to claim 1, further comprising:monitoring the step of applying energy by graphically displaying a mapof a portion of the heart that includes the target tissue and aprogression of energy application along the ablation path.
 6. The methodaccording to claim 5, wherein applying energy further comprisesalternating between a bipolar mode of operation wherein the first andsecond ablation electrodes function as bipolar electrodes and a unipolarmode of operation wherein at least one of the first and second ablationelectrodes functions as a unipolar electrode, and wherein monitoringcardiac electrical activity comprises tagging the map to indicate firstand second portions of the ablation path associated with the bipolarmode of operation and the unipolar mode of operation, respectively. 7.The method according to claim 1, wherein the probe has at least twosensing electrodes disposed between the first and second ablationelectrodes. 8-13. (canceled)